Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
1999-04-15
2001-08-28
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
C347S014000, C347S023000
Reexamination Certificate
active
06281908
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of printing using an ink jet printer, and more particularly, to a method of compensating for skewed printing using an inkjet printer.
2. Description of the Prior Art
Ink jet printers typically include a printhead which is carried by a carriage assembly which is moved in transverse directions across the print medium, relative to the advance direction of the print medium within the printer. For a mono-color printhead used to jet a single color ink onto the print medium, the printhead is scanned across the print medium in one transverse direction, advanced a distance corresponding to the height of the printhead, and scanned in a return direction back across the print medium in an opposite direction. Ink is jetted from the ink emitting orifices in the printhead as the printhead scans in the transverse directions across the print medium. An image area is defined via software which overlies the print medium. The image area includes a plurality of rows of pixel locations and a plurality of columns of pixel locations. As each ink emitting orifice is scanned across an associated pixel location on the image area, a determination is made as to whether ink is to be jetted from the associated ink emitting orifice onto the print medium at the selected pixel location. By sequentially scanning the printhead across the print medium and advancing the print medium during scans a distance corresponding to the height of the printhead, ink may be selectively jetted onto the print medium at any pixel location within the image area.
One known type of error associated with ink jet printing is referred to as a “rotational error” caused by a skewed positioning of the ink emitting orifices relative to the advance direction of the print medium. Such a rotational error may result from rotational inaccuracies of the ink emitting orifices within the nozzle plate on the printhead, rotational errors of the nozzle plate relative to the remainder of the printhead, rotational errors of the printhead relative to the carriage assembly, and rotational errors of the carriage relative to the scanning axis.
A noticeable defect associated with rotational errors is an offset in the transverse direction between vertically adjacent scans of the printhead across the print medium. For example, to print a vertical line, the printhead is scanned in a first transverse direction and the ink jetting heaters are fired at selected points in time corresponding to a column of pixel locations on the image area. The paper is then advanced a distance corresponding to the height of the printhead and the printhead is scanned in an opposite direction and the ink jetting heaters are fired at selected points in time corresponding to the same column of pixel locations on the image area. Since each column of ink dot placement locations on the print medium is in fact rotationally skewed relative to the advance direction, an offset or error in the transverse direction occurs between the bottom-most ink dot placement location of the first scan and the top-most ink dot placement location of the second scan. This offset or error in the transverse direction may be objectionably perceptible to the user, depending upon the severity.
One known method of compensating for rotational errors is to advance or delay the firing times of the ink jetting heaters associated with each ink emitting orifice such that the rotationally skewed column of ink dot placement locations is rotated back to a substantially vertical orientation relative to the advance direction. However, advancing or delaying the firing time associated with each ink emitting orifice such that the entire rotationally skewed array of ink dot placement locations is rotated in one direction or the other requires a substantial amount of computational processing. Such a method therefore requires additional computing time and also may increase the cost of the machine because of the associated electrical processing hardware.
SUMMARY OF THE INVENTION
The present invention provides a method of compensating for skewed printing with an ink jet printer by shifting the position of each swath by a predetermined amount to align the top dots of that swath with the bottom dots of the previously printed swath.
The invention comprises, in one form thereof, a method of compensating for skewed printing on a print medium with an ink jet printer. An image area is defined on the print medium which has a plurality of rows of pixel locations and a plurality of columns of pixel locations. A printhead includes a plurality of vertically adjacent ink emitting orifices arranged in an array having a height. The printhead is scanned during first and second scans across the print medium in directions transverse to the advance direction. The ink is jetted onto the print medium from the ink emitting orifices during the first and second scans at selected ink dot placement locations generally corresponding to one of the columns of pixel locations. An offset is determined in a transverse direction between a bottom ink dot placement location associated with the first scan and a top ink dot placement location associated with the second scan. The position of each swath is shifted by the offset amount to align the top dots of that swath with the bottom dots of the previously printed swath. Note that the offset is a fixed value computed and loaded into memory once and used throughout.
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Gibson Bruce David
Ubellacker Kent Lee
Barlow John
Lexmark International Inc.
Needle & Rosenberg P.C.
Stewart Jr. Charles W.
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